1. Field of the Invention
The present invention relates to a cordless telephone apparatus that informs a user of a state of charging.
2. Discussion of Related Art
When a cordless telephone apparatus is charged, the cordless telephone apparatus is placed on (in) a charger. As the cordless telephone apparatus is closer to the charger, a howling (an acoustic feedback) may occur. Therefore, in relation to an invention which prevents the howling, there has been recently developed a technique to determine whether the cordless telephone apparatus is close to the charger, as disclosed in Patent Document 1 (JP-A-7-221825), for example.
Whether the cordless telephone apparatus is close to the charger is determined as follows. When a detection coil detects an alternating magnetic field generated by a magnetizing coil provided in the charger, an alternating voltage which generates at opposite ends of the detection coil is inputted into a rectification circuit by electromagnetic induction, and an output voltage diverged from the rectification circuit is inputted into a comparator. Then the comparator compares the output voltage with a reference voltage value, so that it is determined whether the cordless telephone apparatus is close to the charger.
However, in the above-mentioned technique, since the comparator is used for comparing direct voltage converted from alternating voltage with the reference voltage value, only two states can be determined, one of the states being that the cordless telephone apparatus is close to the charger and the other being that the cordless telephone apparatus is not close thereto. Therefore, in a case where the determination technique is applied to a determination of a state of charging, only two states of charging, such as a charging-operable state and a charging-inoperable state, can be determined. In other words, as long as the cordless telephone apparatus is placed on the charger, it is always determined that the cordless telephone apparatus is in the charging-operable state.
Even when the cordless telephone apparatus is placed on the charger, a required time for charging is increased, or a charging operation becomes inoperable, when, in a contact-type charging, a foreign matter exists between a charging terminal of the cordless telephone apparatus and a charging terminal of the charger, or the charging terminal of the cordless telephone apparatus is misaligned with, or in a lifted position relative to (from), the charging terminal of the charger, or when, in a non-contact charging, a foreign matter exists between the cordless telephone apparatus and the charger, or the coil of the cordless telephone apparatus is misaligned with, or in a lifted position relative to the coil of the charger. In the above-mentioned technique, however, it is impossible to properly inform a user of the state of charging. Further, even when the cordless telephone apparatus is correctly placed on the charger, the required time for charging is increased, or the charging operation becomes inoperable, when a coating is formed over at least one of the charging terminals in the contact-type charging. In the above-mentioned technique, however, it is impossible to properly inform the user of the state of charging.